The present invention relates generally to paper making machines and, more particularly, to a supporting beam for a paper machine foil or the like, in particular for supporting a so-called single blade foil, the supporting beam being constituted by a horizontal box-type beam having a height dimension of about 1.3 to 2.5 times the breadth of the beam and wherein the side walls of the beam are situated in respective planes which are substantially perpendicular to the direction of travel of the paper machine wire against which the foil supported by the beam rubs.
In the forming sections of conventional paper machines such, for example, as in the Fourdrinier wire section of a paper machine, foils are employed for dewatering the web supported on the wire, such foils being supported on a supporting beam which extends in the cross-machine direction. Box-type beams, i.e., hollow beams having substantially rectangular cross-sections, are often used as such foil supporting means. A box-type beam for supporting a paper machine foil or the like usually has a height of about 1.3 to 2.5 times the horizontal breadth of the beam. A holder device is provided on the upper part of the beam in which the foil list, or blade of the foil, is fixed.
Since the foil supporting beam generally constitutes the most slender or narrowest beam of the entire wire section, such beams are particularly susceptible to vibrations which most often are caused by the friction forces present between the foil and the paper machine wire passing thereover. These vibrations are particularly harmful since they tend to create disturbances in the web formation. Moreover, the vibrations tend to propogate through the frame structure of the wire section so as to set up corresponding vibrations in other pieces of equipment which may cause serious problems in their operation. In fact in extreme cases, the vibrations set up in the foil supporting beam can shatter a ceramic foil list.
Attempts have been made to reduce the vibrations of foil supporting beams by forming the upper part of the beam so as to be inclined in the direction of web travel. In this regard, reference is made to U.S. Pat. No. 3,762,991 assigned to Beloit Corporation of Beloit, Wis. It is stated in this patent that it is favorable to provide the frame of the foil beam such that upon the beam being deflected due to the effect of the horizontal friction force created between the wire and the foil list, that the extent of the beam's deflection is about 0.degree. to 5.degree. in a downwardly slanted direction. It is noted in the patent that by this provision the tendency of the beam to vibrate is reduced. However, the arrangement disclosed in the above-mentioned patent has the drawback that the inclination of the beam necessarily increases the space requirements for the foil in the lateral direction consequently resulting in the fact that fewer foil beams can be accommodated on a given horizontal run of the wire. Another drawback of the arrangement disclosed in this patent is a greater difficulty in the manufacture of such an inclined beam and the fact that the inclined position of the front side wall of the foil beam tends to increase splashing of water back into the paper maching wire.